Hello! While it is true that his endlag is very small, the startup is some of the worst, leaving him opened to be pressured to fast attacks up close. His aerials are also a huge commitment as he can usually only do one per jump, try to stay well out of his way and harass him with projectiles and punish every wiffed aerial you can. It'll be an uphill battle; Yink has a lot of multi-hit moves and Shulk can just tack on shield art in between hits and even punish you for landing them.
So in summery, keep your distance (more than you would most characters) and apply pressure with projectiles. Don't shield his attacks, if you do, and you'll probably have to when he switches to speed, don't punish unless he spaces poorly, punished wiffed aerials but before he lands. Finally, try and bait out shield art and only try and kill him when it's gone.
Hope I've helped, it's been a while since you asked.